The invention relates generally to electrical power conversion systems, and more particularly to control of electrical machines via ac-ac power converter systems.
A range of applications exists for power conversion circuitry, particularly for the control of electrical machines, such as motors. A wide variety of applications, such as air conditioners, blowers and others utilize electrical machines operating at different speeds. These different speeds may be obtained by varying amplitude and/or frequency of the voltage applied to the electrical machine. The amplitude and/or frequency of the voltage applied to the electrical machine can be varied with the help of a power processing stage introduced between the electrical machine and the supply voltage.
For example, power converter systems of various topologies may be employed to achieve speed control of electrical machines via the techniques mentioned above. However, current power converter systems generally inject harmonics into the system and into the electrical distribution grid, and also reduce the power factor of the overall system. To overcome these problems, filters and power factor correction circuits of appropriate size and type are placed at various stages of power conversion process. However, this makes the power converter system bulky and reduces the overall efficiency of the system.
It is therefore desirable to provide an efficient and robust power converter system with minimum components and simple control techniques that ensure better input power quality performance and high power factor.